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Percentage Conversion (percentage + conversion)

Distribution by Scientific Domains

Polymers and Materials Science	75%

Selected Abstracts

Solid acid clay mediated copolymerization of methyl acrylate and 1-octene: 2D NMR substantiation of predominant alternating comonomer sequence

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 8 2009
Sukhdeep Kaur
Abstract Montmorillionite K10 powder presence during radically initiated copolymerization of methyl acrylate (M) and 1-octene (O) gave copolymers with higher incorporation of alkene unit. Highly viscous and transparent copolymers showed alternation irrespective of the copolymer composition. Increasing the amount of K10 powder increased the total percentage conversion, as well as 1-octene incorporation. The monomodal curves obtained in gel permeation chromatography (GPC) substantiated that true copolymers were formed. The alternation in the copolymers was authenticated through Heteronuclear Multiple Quantum Correlation (HMQC) experiments in conjugation with Total Correlated Spectroscopy (TOCSY). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2156,2162, 2009 [source]

Structural investigations of polypropylene glycol (PPG) and isophorone diisocyanate (IPDI)-based polyurethane prepolymer by 1D and 2D NMR spectroscopy

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 6 2005
A. Prabhakar
Abstract Polyurethane prepolymers are widely used in reactive hot melt adhesives and moisture cured coatings. NCO-terminated polyurethane of polypropylene glycol (PPG)-1000 and isophoron diisocyanate (IPDI) with an NCO/OH ratio of 1.2:1 were prepared without any catalyst or solvent. 1D and 2D NMR spectroscopy was used for the structural investigation of the synthesized prepolymer. 1H NMR spectra and dibutylamine back-titration were used to monitor the reaction of isocyanate groups with the hydroxyl function of PPG and to allow a good description of the evaluation of the urethane groups. The data on percentage conversion were crosschecked with 13C NMR spectroscopy in the urethane zone for the methanol endcapped prepolymer. The observations show a higher reactivity of the secondary NCO group than of the primary group. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1196,1209, 2005 [source]

Conjugated linoleic acid conversion by dairy bacteria cultured in MRS broth and buffalo milk

LETTERS IN APPLIED MICROBIOLOGY, Issue 5 2007
C.P. Van Nieuwenhove
Abstract Aims:, To evaluate strains of Lactobacilli, Bifidobacteria and Streptococci for their ability to produce conjugated linoleic acid (CLA) from free linoleic acid (LA). Methods and Results:, Eight dairy bacteria tolerant to LA were grown in MRS broth containing LA (200 ,g ml,1) and CLA was assessed. Seven bacteria were able to form CLA after 24 h of incubation, varying percentage conversion between 17% and 36%. Lactobacillus casei, Lactobacillus rhamnosus, Bifidobacterium bifidum and Streptococcus thermophilus showed the highest LA conversion and were inoculated into buffalo milk supplemented with different concentration of LA. The production of CLA at 200 ,g ml,1 of LA was two- or threefold in milk than MRS broth. All evaluated strains were able to produce CLA from high LA levels (1000 ,g ml,1). Conclusions:, The most tolerant strain to LA was Lact. casei. Lacttobacillus rhamnosus produced the maximum level of CLA at high LA concentrations (800 ,g ml,1). The selected bacteria may be considered as adjunct cultures to be included on dairy fermented products manufacture. Low concentration of LA must be added to the medium to enhance CLA formation. Significance and Impact of the Study:, The production of CLA by strains using milks from regional farms as medium offer a possible mechanism to enhance this beneficial compound in dairy products and those the possibility to develop functional foods. [source]

Kinetic and thermodynamic study of methanolysis of poly(ethylene terephthalate) waste powder

POLYMER INTERNATIONAL, Issue 3 2003
S Mishra
Abstract Depolymerization of poly(ethylene terephthalate) waste (PETW) was carried out by methanolysis using zinc acetate in the presence of lead acetate as the catalyst at 120,140,°C in a closed batch reactor. The particle size ranging from 50 to 512.5,µm and the reaction time 60 to 150,min required for methanolysis of PETW were optimized. Optimal percentage conversion of PETW into dimethyl terephthalate (DMT) and ethylene glycol (EG) was 97.8% (at 120,°C) and 100% (at 130 and 140,°C) for the optimal reaction time of 120,min. Yields of DMT and EG were almost equal to PET conversion. EG and DMT were analyzed qualitatively and quantitatively. To avoid oxidation/carbonization during the reaction, methanolysis reactions were carried out below 150,°C. A kinetic model is developed and the experimental data show good agreement with the kinetic model. Rate constants, equilibrium constant, Gibbs free energy, enthalpy and entropy of reaction are also evaluated at 120, 130 and 140,°C. The methanolysis rate constant of the reaction at 140,°C (10.3 atm) was 1.4,×,10,3,g PET mol,1 min,1. The activation energy and the frequency factor for methanolysis of PETW were 95.31,kJ,mol,1 and 107.1,g PET mol,1 min,1, respectively. © 2003 Society of Chemical Industry [source]